Merocyanine dye-sensitized photographic materials comprising silver halide emulsion layers containing azo-dyes



United States Patent "ice 3 Claims. 61. 96-99) ABSTRACT OF THE DISCLOSURE Particularly desirable sensitization of silver-dye-bleach silver halide emulsions is effected with certain substituted merocyanine dyes.

This invention relates to a merocyanine dye-sensitized photographic element comprising at least one silver halide emulsion layer uniformly dyed with an azo-dye for use in the silver dye bleach process.

Colored photographic images can be prepared by the silver dye bleach process in which a negative or a positive silver image is obtained, depending on the processing, by exposure and subsequent development of uniformly colored photographic layers. After further treatment, such as fixing and subsequent hardening, the azo-dye is bleached, generally in a strongly acidic bleach bath, in accordance with the silver image. In this way, dye image of the original is obtained. The dye image has a gradation opposite to the gradation of the silver image. The dyes generally employed are azo dyes, both water-soluble dyes and insoluble pigments.

One of the great disadvantages of the silver dye bleach process is that the sensitivity of the dyed photographic layers is very considerably reduced. This occurs in particular if the layers are sensitized in such a way, as is generally the case, that the blue-sensitive layer is dyed yellow, the green-sensitive layer magenta and the red-sensitive layer cyan. The reason for this is that the sensitization maxima coincide with the absorption maxima of the dyes. With respect to the sensitivity of the light-sensitive layers, the silver dye bleach process is inferior to other color photographic processes. Accordingly, one of the great difiiculties of the silver dye bleach process is the preparation of sufficiently sensitive layers. 4

The sensitivity of photographic emulsions can be increased by the addition of suitable sensitizers. Sensitizers which are to be used in materials for the silver dye bleach process have to satisfy several requirements. In addition to good sensitizing properties the sensitizer must not deleteriously effect the stability of the emulsions, particularly in storage and under tropical conditions. Furthermore the sensitizing dyes have to be sufliciently soluble in the processing baths, so that the dye is readily washed out and no coloring of the support, for example paper,- or the binding agent of the layer, for example gelatin, occurs. Furthermore, the sensitizer must adhere sufficiently firmly to the silver halide grains as not to be displaced by the azo-dyes, because otherwi-se the sensitizing action is decreased in the presence of vazo-dyes. In particular because of the last mentioned requirement manyof the sensitizers, which are operative in conventional silver halide photographic materials, are not suitable for the silver dye bleach process.

For instance basic cyanines are readily detached or removed from the silver halide grain by azo-dyes containing sulfonic acid groups and, for this reason, are not sufliciently effective in the silver dye bleach process. In

, 3,401,404 Patented Sept. 10, 1968 some cases even a desen-sitizing effect can be observed of compounds which act as sensitizers in conventional photographic processes. It is known to employ betaine cyanines as sensitizers for photographic layers for use in the silver bleach process. These sensitizers are, however, of limited utility since they cannot be washed out sufiiciently in the processing baths so that theimage portions remain slightly discolored.

It is an object of the invention to provide sensitizing dyes for silver halide emulsion layers to be used in the silver dye bleach process. Another object is to provide photographic materials comprising at least one lightsensitive silver halide emulsion layer optically sensitized and containing an azo-dye. Other objects will become apparent from a consideration of the following description and examples.

We now have found that a particular class of merocyanine dyes are outstanding in their optically sensitizing properties for silver halide emulsion layers which contain uniformly distributed azo-dyes and which are to be used in the silver dye bleach process. The merocyanines of the present invention are characterized by two 5- or 6-membered heterocyclic rings which contain nitrogen as a ring member and which are linked together by way of 2 or 4 methine groups. Merocyanines of this type are generally known as zero-, dior tetramethine merocyanines.

Particularly suitable are merocyanines of the following formula:

wherein:

X =represents the ring members necessary to complete a 5- or 6-membered heterocyclic ring, preferably of the following groups: thiazole, benzthiazole, napthothiazole, oxazole, benzoxazole, naphthoxazole, selenazole, benzselenazole, naphthoselenazole, benzirnidazole, indoline, pyrrolidine, tetrazole, thiodiazole;

Y=hydrogen or alkyl preferably lower alkyl having up to 3 carbon atoms, such as methyl or ethyl;

Z=the ring members necessary for completing a S-membered heterocyclic ring preferably such as thiazole oxazole, selenazole, imidazole or pyrazole;

R=alkyl preferably lower alkyl having up to 5 carbon atoms in particular methyl or ethyl, whereby the alkyl groups can be substituted by carboxy, sulfo, hydroxy or chlorine;

R'=alkyl preferably alkyl up to 5 carbon atoms such as methyl or ethyl, olefinically unsaturated alkyl, preferably up to 5 carbon atoms such as allyl, cyeloalkyl such as cyclohexyl, or aryl preferably phenyl;

n=0 or 1.

The above heterocyclic or aromatic rings can be substituted, for example, with alkyl preferably lower alkyl of up to 5 carbon atoms, alkoxy having up to 5 carbon atoms, hydroxy or halogen preferably chlorine.

.The merocyanine dyes of the present invention .are outstanding in their optically sensitizing action' for silver halide emulsion layers containing an azo-dye. Furthermore they are superior to betain cyanines since the color images obtained by the process of the invention show very clear white portions of the images without any color stain.

The above merocyanines are substantially inert both to the azo-dyes in the photographic layers for the silver dye bleach process and to other additives, in particular stabilizers, mordants such as biguanides or guanides, wetting agents, agents for influencing the viscosity of azo-dyes in gelatin and/or photographic emulsions, hardening agents such as chrome alum, paraformaldehyde, or plasticizers such as glycerol.

The merocyanines of the instant invention are Well known and described in the handbook of F. M. Hamer, The Cyanine Dyes and Related Compounds, published by Interscience Publishers (1964), chapter XIV.

In the preparation of photographic emulsions the merocyanine dyes of the invention are preferably incorporated in the washed, finished silver halide emulsions before the azo-dyes are added and should be uniformly distributed throughout the emulsion. The methods of incorporating sensitizing dyes in light-sensitive emulsions are well known to those skilled in the art of emulsion making. Generally it is convenient to add the sensitizing dyes from solutions in appropriate solvents that should have no deleterious effect on the light-sensitive materials. Lower aliphatic alcohols such as methanol, ethanol or isopropanol, furthermore pyridine and the like, alone or in admixtures, =for example with water, have proven satisfac tory as solvents.

The silver halides of the emulsions comprise silver Example 1 500 g. of a silver bromide emulsion of average sensitivity are sensitized with mg. of a dyestufi of the formula dissolved in methanol. The preparation of the sensitizer is described in- French patent specification No. 1,133,324. In addition to the usual coating additives and hardening agents, an aqueous solution containing gelatin and 4 g.

chloride, silver bromide or silver chlorobromide which of a yellow dyestulf of the formula SOSH: may contain a small amount of silver iodide, preferably as described in British patent specification No. 766,020,

not more than 10 mol percent.

The type of silver halide emulsions that can be sensitized with the merocyanines of the present invention include any of those prepared with hydrophilic colloids that are known to be satisfactory for dispersing silver halides. These colloids include preferably gelatin which can be used in admixture with other hydrophilic colloids such as albumin, alginic acids and derivatives thereof, hydrophilic synthetic resins such as polyvinyl alcohol, polyvinyl pyrrolidone and the like.

The concentration of the merocyanine dye and the light-sensitive emulsion can vary widely from about 5 to about 100 mg. per liter of emulsion. The suitable and most economical concentration for any given emulsion will be apparent to those skilled in the art upon making the tests customarily used in the art of emulsion making.

To prepare a silver halide emulsion sensitized with a merocyanine of the present invention, the following procedure is satisfactory: The desired quantity of the sensitizing dye is dissolved in a suitable solvent and a volume of this solution containing the desired amount of the dye is slowly added to the silver halide emulsion. Thereafter, the azo-dye is added preferably from a solution in a suitable solvent. With most of the merocyanine dyes of the present invention 10-30 mgs. of sensitizing dye per liter of emulsion are suflicient to produce the maximum sensitizing effect. The photographic emulsions may be coated on any of the photographic supports including paper, cellulose esters such as cellulose acetate or nitrate, polystyrene, polyesters in particular of polyethylene terephthalate, poly carbonates, preferably of bis-hydroxy phenyl alkanes, and the like.

Photographic silver halide emulsions containing the merocyanines of the invention can also contain such additives as chemical sensitizers, for instance, sulfo sensitizers, nobel metal compounds such as gold or palladium compounds, stabilizers such as benzotriazole compounds, heterocyclic mercapto compounds, mercury compounds or azaindenes; hardeners such as glyoxal, formaldehyde, acrolein or the like.

Azo-dyes which can advantageously be used in combination with the merocyanines of the invention comprise the customarily employed dyes which are known to be satisfactory for the silver d-ye bleach process. Preferred Example 1, is added to the emulsion. The emulsion is then mordanted with 2 g. of diphenyl-4-4-dibiguanide, as described in French patent specification No. 864,332 to increase the resistance to diffusion of the dye, and applied onto a baryta-coated paper. The resulting layer contains p-Methyl aminophenol g 1 Sodium sulfite anhydrous g 13 Hydroquinone g 3 Sodium carbonate (anhydrous) g 26 Potassium bromide g 1 Water ml 1000 (2) Rinsing for 1 minute.

(3) Fixing for 5 minutes in the following composition:

Sodium thiosulfate g 200 Potassium metabisulfite g 20 Water ml 1000 (4) Rinsing for 5 minutes.

(5) Hardening by treatment in a 4% aqueous formaldehyde solution for 5 minutes.

(6) Rinsing for 5 minutes.

(7) Bleaching of the azo-dye by treatment in the following solution for 20 minutes:

Ethanol ml 50 Thiourea g 50 Concentrated sulfuric acid ml 5 2,3-dimethyl quinoxaline mg Water ml 910 (8) Rinsing for 5 minutes. (9) Bleach-fixing for 15 minutes in the following bath:

Tetrasodium ethylenediaminetetraacetate g 26 Sodium carbonate (anhydrous) g 24 Ferric chloride g 15 Sodium sulfite (anhydrous) g 13 Sodium thiosulfate g 200 Water ml 500 6 Final rinsing for minutes. (prepared according to German Patent No. 883,025) and with 300 ml. of a 1% aqueous solution of the mordanted azo-dye referred to in Example 1. The processingis performed as described in Example 1. The sensitized sample is more sensitive by 1.1 logarithmic units than the unsensitized emulsion.

Two direct-positive color wedges are formed which are measured behind a blue filter. The difference in the sensitivity is 1.7 logarithmic units. The paper support is unstained.

Example 2 After melting with a small amount of 4-hydroxy-6- methyl-1,3,3a,7-tetraazainden as a stabilizer, 500 g. of a highly sensitive silver iodobromide emulsion is sensitized 10 to green light by adding 15 mg. of the sensitizing dye of the formula Example 5 The procedure is the same as in Example 2, except that the dye used in that example is replaced by 15 mg. of the sensitizer of the formula the preparation of which is described in Belgian patent o0 specification 648,068. The usual additives are then incorporated, followed by the addition of 200 ml. of a 1% which y e P p in accordance wi h Bri i h Pataqueous solution of the magenta azo dye of the formula ents Nos. 426,718 and 428,360.

CH3 CH3 I o1- S0 -Il IH ()H H3O (EH; 1110 HlTI-SOg- -o1 I CH CH3 N=N- C N= N H3 Hots SO3H I H Hols so3rr 113c- -CH,

which is prepared in accordance with German patent The material is processed as described in Example 2. specification No. 1,039,840. To improve its fastness to The sensitized sample has a sensitivity higher by 1.2 difiusion, a solution of 0.75 g. of bis-[3-anisidyl-4-bigualogarithmic units than that of the unsensitized sample. nide] is added, and the emulsion is applied onto a support Example 6 of cellulose triacetate as described in Example 1. A sample 40 is exposed in ra sensitometer behind a step wedge and yel- The Pfh r h me as In Example 2, except that low filter, and is then processed as describedinExample 1 the Sehslhlef used In that example 15 replaced y 15 and compared with a standard sample which is not senof the y of the formula sitized by sensitometric measurement behind a green filter the difference in the sensitivity of the two samples CH3 is found to be 1.7 logarithmic units. In the sensitized & C

- Ha sample, the support is practically free from any colormg. v

' Example 3 N =CHCH=((jC=0 I HaC- N The procedure is the same as in Example 2, except that (1:113 N I the sensitizer used in-Example. 2 is replaced by 15 mg. of a sensitizing dye of the formula H v which may be prepared as described in British Patent No. C" l i 428,360. Contrary to Example 2, no mordant is used. I The material is processed as described in Example 1. C=CH,CH=C- NH The sensitized sample has a sensitivity of 0.73 logarithmic 0: 2 units greater than the unsensitized sample.

Example 7 brr N I JHQ v If the sensitizer referred to in Example 2 is'replaced by I After exposure, processing and evaluation as in Ex- .5 mg-Of the dye ample2, the difiF erence in sensitivity between the sensitized and unsensitized layers is 0.9 logarithmic units. 1 CHCH (IIH;

Example 4 a (3E2 J=oH o=c-- s 500 g. of a silver chloride emulsion are mixed as de- N i scribed in Example 1 with 15 mg. of the dye of the for- (Q I N mula H (FEE- 2 I 1 CH; C CHCH'=C-N- C s which may be obtained according to German Patent'No. N J 4:: I 883,025 and if the procedure described in Example 2 is 5 followed, the resulting sensitized sample has a sensitivity 3 V I 1.1 logarithmic units higher than that of the unsensitized sample.

7 Example 8 If the sensitizer mentioned in Example 2 is replaced by 15 mg. of the compound of the formula which may be prepared according to J. Am. Chem. Soc. 73, 5332 (1951 and if the procedure described in Example 2 is followed, there is an increase in the sensitivity of the sensitized sample of 0.82 logarithmic units as compared with an identical unsensitized emulsion.

Example 9 The procedure is the same as in Example 2, except that the emulsion has a high silver content and, to obtain a suitable -value, is diluted with such a quantity of gelatin, that, after exposure and development, there is still sufiicient silver left to bleach the azo-dye completely. A sensitizing dye of the formula HaO-Q-SOz-NH H 8 Example The procedure is the same as in Example 9, except that the sensitizer dye has the formula 50:13: A simple is exposed and processed as described above. The sensitized sample is 1.4 logarithmic u-nits more sensitive than an unsensitized comparison sample.

The sensitizing dye is prepared as follows:

5 g. of 1-methyl-2-methylmercapto-S,6-dichlorobenzimid-azole are heated at 130 C. for minutes with 4 g. of propane sultone. After cooling to 100 C. the melt is dissolved in ml. of pyridine while stirring. The resulting solution is stirred for 24 hours at 20 C. with 2 g. of 3-ethyl-5-ethylidene rhodanine and 6 ml. of triethylamine. The dye which crystallizes out is suction-filtered, dissolved in water and repreciptated with NaCl solution. It is then recrystallized from 700 ml. of methanol/ chloroform (1:1). Yield: 0.5 g.; M.P. about 300 C.

Example 11 15 mg. of the sensitizing dye of the formula which is prepared by a method analogous to that described in J. Am. Chem. Soc. 73, 5337 (1951) Merodicarbocyanine are added to 500 ml. of a highly sensitive silver bromide emulsion containing 50 mg. of 1-phenyl-5- mercapto tetrazole as a stabilizer. After the addition of hardening agents such as 0.4 g. of chrome alum and 0.3 g. of paraformaldehyde, and wetting agents such as 20 ml. of a 5% solution of saponin the emulsion is mixed with 250 ml. of an aqeuous gelatin solution containing 1% of the cyan dye of the formula I I )11 NH-SOz-GCH:

HOaS -SOaH HOaS :13:

and propane sultone are heated at 100 C. for 1 hour with 25 g. of diphenyl formamidine and m1. of acetic anhydride.

The reaction solution is taken up in acetone and the 2 (phenylacetamino-ethylide-ne)-intermediate product which crystallizes out, is suction-filtered. Yield: 22.2 g. M.P. 286 C.

4 g. of this intermediate product are condensed for 3 hours on a steam bath with 3 g. of 1,3-dimethyl thiohydantoin in 20 ml. of cresol and 15 ml. of pyridine with 6 ml. of triethylamine. The resulting dye is dissolved in water and precipitated with potassium iodide. It is recrystallized from 150 ml. of water. Yield: 1.3 g.; M.P. above 290 C.

which is obtained from 3,3'-ditheoxy-4,4'-diamino diphenyl by diazotisation and coupling with p-tosyl H acid. The dye is made resistant to diffusion 'by adding 0.5 g. of bis-(3-anisidyl-4-biguanide) in a 1% aqueous gelatin solution, and applied onto a baryta-coated paper base. The dried layer contains 1.5 g. of silver per square meter as silver halide. For comparison purposes, an otherwise iden- Example 12 solution). In this case an acidic thiosulfate both containing for instance 200 g. of sodium thiosulfate and The procedure ls the Same as m Examp 1e except that 20 g. of potassium metabisulfite per liter of solution, will the azo dye is replaced by the following cyan dye:

which is itself highly resistant to diffusion and, for this generally be used as a fixer. Combined bleaching and reason, does not require mordanting. This compound is fixing baths are also very useful, however, and an exprepared in accordance with Example 1 of German Pat- 15 ample of such a composition comprising an Fe(III)-come t N 1,041,355, The comparison s d i n f m plex of ethylene diamine tetraacetic acid is described in which the mordant, bis-(3-anisidyl-4-biguanide), has also Example 1. been omitted. The samples are processed as described in We claim: Example 11. According to the measurement of the cyan 1- A lightensitive photographic element, comprising colored wedges obtained the en iti ed a le i m re at least one supported light-sensitive silver-dye-bleach itiv by 1,87 logaritmic it silver halide emulsion layer which contains a silver-dye- In the above examples differences in sensitivity are given blfiach 3Z0 dye and is sensitized y a sensitizing amount in logarthmic units wherein a difference of sensitivty of of a merocyanine y of the formula 0.3 log. units correspond to a difference by a factor of 2 and 1.0 log. units correspond to a difference by a factor Y of 10. -N n C 5 As has been mentioned before the essential steps of the processing of silver dye bleach materials consist in development of a silver image, bleaching of the dye according to the silver image and removing residual silver and wherein! silver halide by a bleaching and a fixing bath, both of X represents the ring members necessary to complete a which can be combined in one composition. Between tetralole, benlthialole, indoline! PY befllimiddeveloper and dye bleach bath other steps such as fixing azole, thiadiazole or benzoxazole g;

or hardening baths can be included. n Y stands for hydrogen or alkyl having up to 3 carbon As developer compositions those containing for instance atoms;

p-methyl aminophenol and hydroquinone may be used but Z stands for the ring members necessary for completing other systems especially those containing l phenyl pyra rhodanine, thiohydamoi or Pyrazolone ring;

lid are l f L R stands for alkyl having up to 5 carbon atoms, carboxy- For the purpose of the inv t a Wide variety of substituted alkyl in which the alkyl has up to 5 carbon azo dye bleaching baths can be used They may contain 40 atoms, sulfa-substituted alkyl having up to 5 carbon fr 10 to 80 f thiouwa, 20 to 30 ghof an alkali atoms, hydroxy-substituted alkyl having up to 5 carbon halide and 10 to 20 g. of a mineral acid per liter such atoms or chloro'substimted alkyl having P to 5 as described in U.S. Patent No. 2,217,544. Other variations boll atoms;

than those indicated are possible, including the omission represents alkyl having P to carbon atoms: W

of halide and the addition of organic solvents. Further- Pexyl or Phenyl and more, dye bleaching baths on the basis of quinoline, hypo- 1S 0 phosphite, iodide and mineral acid as described in U.S. A hght'sensltlve PhotograPhic element as defined in Patent No. 29 5 or combinations of iron salts and claim 1 wherein X and Z are substituted with alkyl having isothiocyanates are also useful. Besides the basic ingredito 5 carbon atoms Plkoxy having I? to 5 carbon ents mentioned above, the bleaching bath in question atoms ,chlonner normally also contains bleaching catalysts such as 2,3- The comblflatlon of clam 1 in which the Z dimethyl quinoxaline or other quinoxaline derivatives, Plates a rhodanme ring and is unsubstituted- 2-amino-3-hydroxy phenazine, 2,3-diamino phen-azine,

azines, oxazines, thiazines, cinnolines, indophenazines, References C'ted ferroor thienoquinoxalines and the like, which are usualv UNITED STATES PATENTS ly added in amounts from 2 to 3 00 mg. per liter of bleach- 2, 12,44 9 1952 Gaspar et 1 9 73 ing solution. Silver bleach baths for use in the process 3,053,655 9/ 1962 Dreyfuss et a1 96-99 of the process of the invention may, e.g., consist of copper 3,157,507 ll/ 1964 Bruengger et al 9699 chloride (10 to 50 g.) and potassium bromide (10-100 g.) together with hydrochloric acid (5 to 20 ml. per liter of TRAVIS BROWN, Primary Examiner- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,401 ,404 September 10 I968 Bernhard Seidel et a1 It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 10, lines 24 to 29, the right-hand portion of the formula should appear as shown below:

Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

